β-Glucosidase enzymatic activity of crystal polypeptide of the Bacillus thuringiensis strain 1.1

Abstract

The crystals of Bacillus thuringiensis strain 1.1 consist of the 140 kDa δ-endotoxin, which exhibits β-glucosidase enzymatic activity, based on the following data. (i) Purified crystals exhibit β-glucosidase enzymatic activity. When the crystals are reacted with specific antibodies directed either against the commercial (almond purified) β-glucosidase or against the 140 kDa polypeptide, then considerable reduction of enzymatic activity is observed almost at the same level with both antibodies. (ii) Commercial β-glucosidase and the 140 kDa crystal polypeptide share antigenic similarities; in Western immunoblots, the 140 kDa crystal polypeptide is recognized by anti-β -glucosidase antibodies, and commercial β-glucosidase is recognized by anti-140-kDa antibodies. (iii) The enzymatic properties of commercial β-glucosidase and that resident in the crystals of B. thuringiensis strain 1.1 are very similar. Thus, both enzymes hydrolyze a wide range of substrates (aryl-β -glucosides, disaccharides with α- or β-linkage polysaccharides) and have an optimum activity at 40°C and pH 5. Both enzymes are relatively thermostable and are resistant to end-product inhibition by glucose. Additionally, they show the same pattern of inhibition or activation by several chemical compounds. (iv) The crystals and commercial β-glucosidase show almost equivalent levels of insecticidal activity against Drosophila melanogaster larvae and, furthermore, cause reduction in adult flies that emerge from larvae surviving treatment.